A worried man has turned to the internet for advice after discovering his girlfriend 'stealing' his sperm after sex.

The baffled boyfriend from New York revealed on Reddit that he had gone to the bathroom after having sex with his girlfriend, and returned to find her 'pouring the contents of a used condom inside her vagina'.

Asking if anyone knew if what she'd done was legal, he added: I'm nervous as f*** honestly.'

And it appears the unfortunate man may not have the law on his side.

Despite being obviously morally wrong, the US legal system considers the passing of sperm during sex ‘a gift’ even if it was not intended.

A series of cases have found that it cannot be classed as theft, including one couple who had a baby after the woman kept semen after they had oral sex then used it to get pregnant.

The Reddit post, which gained over 12,500 upvotes, prompted other users to react with horror.

One wrote: 'Well, number one I would assume that she is now your ex-girlfriend? Stay away from her and if she tells you that she is pregnant, get a paternity test.'

The user stunned Reddit with his revelation as others warned him to dump his girlfriend (stock image)

Elaborating on their relationship, the man explained: 'My girlfriend and I are both late 20s. About an hour ago we had sex. She is not on the pill, so we use condoms.

'I had just finished and removed the condom and I went to the bathroom after that. She screamed at me to the bathroom "peeing or pooping?", which I thought was weird.

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On his return, the man discovered what she was up to and tried to pull the condom away.

The user's full post on the Reddit forum detailed the young man's troubles, as he begged for advice from others on what he should do next

'She started screaming bloody murder and screaming "rape". I had to leave her alone before someone in my apartment hears and calls the police,' he said.

He then begged other users for legal advice, writing: 'Is this legal at all? What happens if she gets pregnant?

'I did not consent to her doing this - do I legally own my sperm and what are the odds of her getting pregnant?'

Is 'stealing' sperm against the law?

According to the law in the US, if you have consented to having sex, the law considers that to be consent for the consequences thereof, including at least 18 years of child support payments.

The case of Hermesmann v. Seyer (1993) set the precedent in Kansas, where it was settled the woman could still sue the father of her child for child support even if conception occurred as a result of a criminal act committed by the woman.

In the past it has also been ruled that the kind of act can't be claimed as theft as sperm could be seen as a gift from one person to another.

That was the case for one couple in Chicago in 2005.

Dr Richard Phillips accused Dr. Sharon Irons of a "calculated, profound personal betrayal" after an affair, saying she secretly kept semen after they had oral sex, then used it to get pregnant.

The court decided that although it had caused him extreme emotional distress, Dr Phillips should pay child support for their five year old child.

"Dr Sharon Irons [She] asserts that when plaintiff 'delivered' his sperm, it was a gift - an absolute and irrevocable transfer of title to property from a donor to a donee," the decision said. "There was no agreement that the original deposit would be returned upon request."

Reddit users reacted with horror at the post, begging him to break up with his girlfriend and seek legal advice

One user recommended getting legal advice, stating: 'Document this - make detailed notes to yourself describing what you observed, and write the date/time of the events, and the date/time you wrote those notes.

'If she gets pregnant, she carries the child to term, and a paternity test proves the baby's yours, get a lawyer. The lawyer may be able to help you sue for full custody if you want that, or for termination for paternal rights.'

Another also suggested a paternity test, saying: 'Cut the crazy out of your life immediately. Do not contact her in any way. If she claims to be pregnant demand a paternity test.'